Understanding and fixing plug socket outlets

Most electrical appliances can be plugged in at any socket outlet, which may be sunk in the wall or surface mounted. Permanently fixed appliances, such as cooker hoods, are connected directly to the power circuit using fused connection units (FCUs), which are protected by a dedicated fuse.

Use a mains tester unit to check each socket outlet in turn.

Up to three lights will come on in different combinations to indicate that the socket is correctly wired or that it has a fault. Check the chart on the back of the tester (or the tester manufacturer's instructions) to identify specific faults. Test once a year.

Worn or damaged outlet: Replace socket outlet (see below).

Cable disconnected inside outlet: Turn off mains and check that connections to terminals are securely made. 

Dirt in connectors of switch: Replace socket outlet. 

Consumer unit fuse blown or MCB tripped: Trace and rectify fault. Replace fuse or switch MCB back on. 

Turn off the main power switch and also remove the fuse of turn odd the miniature circuit breaker (MCB) for the circuit on which you are working. Then switch the power back on to the other circuits.

Test the socket outlet with a lamp to make sure the power is off. Undo the screws holding the faceplate in place and pull it away from the mounting box.

A socket outlet on a ring main has two wires in each terminal.

If there is one wire in each terminal, the outlet is a spur (ie it is wired to a socket that is itself on the ring main). If there are three, it supplies a spur: connect the new outlet in exactly the same way as the old one—red to live, black to neutral and green/yellow to earth.

Reconnect the earth link between the faceplate and mounting box, as shown.

Make sure that none of the wires will be twisted or caught as you fold them back into the box.

If the earth link is missing, use the earth wire from a cable offcut to create an earth link. If earth wires are bare, cover them with a green/yellow sleeving. Screw the faceplate back on and then replace the fuse or reset the MCB and switch the power on.

Test the socket with a mains tester before use.